1. Technical Field
The present invention relates to direct access storage devices in general, and in particular to hard disk drives. Still more particularly, the present invention relates to a method for registering a defect map within a hard disk drive.
2. Description of the Related Art
Hard disk drives are often used to store data processed by a computer system. A hard disk drive typically has a recording disk and a head for reading/writing data from/to the recording disk. The head accesses a target sector of the recording disk so as to read/write data therefrom/thereto. In the case where the surface of a recording disk is damaged during fabrication, some sectors in the damaged portion are often incapable of reading/writing data therefrom/thereto. That is why a read/write test must be performed on each recording disk within a hard disk drive before delivery so that any sector that does not satisfy a predefined standard is registered as an unusable sector. The positional information of all unusable sectors for each recording disk within a hard disk drive are then generated, which is commonly referred to as a defect map. The defect map is stored in a specific area of the recording disk.
During the startup process of a hard disk drive, the above-mentioned defect map is read from the recording disk and transferred to a system memory. Before data is to be read/written from/to the recording disk according to a command from a host computer, the defect map stored in the system memory is referenced in order to avoid the unusable sectors being accessed.
Some of the conventional defect maps include the “position” information registered with respect to each of the unusable sectors. In other words, unusable sectors are registered one by one in a defect map (hereinafter, this method will be referred to as the point registration method). However, the problem with such method is that each defect map grows as the number of unusable sectors increases. In order to avoid such a problem, some defect maps are designed to register the “position” of each unusable sector and the “number” of consecutive unusable sectors. Specifically, multiple consecutive unusable sectors is recognized linearly and both position and length information items are registered (hereinafter, this method will be referred to as the line registration method).
For example, a recording disk 1, as shown in FIG. 11(a), is damaged by a scratch A, and scratch A is extended over several sectors S in a track T, as shown in the expanded view of FIG. 11(b). Thus, those sectors often become unusable. In such a case, the above-described line registration method can assume the information about multiple unusable sectors S continued in a track T as one information item. As a result, the amount of information in a defect map can be reduced over the point registration method.
Sometimes, however, the line registration method is not the most cost effective method for recording scratch A that is extended over several tracks T, as shown in FIG. 11(b). This is because the recording density of disks has improved tremendously in recent years, and the distance between tracks T becomes shorter. Accordingly, unusable sectors S come to be generated in more tracks T, as shown in FIG. 11(c), even when the size of scratch A remains the same. As a result, the amount of data recorded in a defect map also increases proportionally with the increase in recording density of disks. When the size of a defect map increases, buffer areas for storing defect maps decrease proportionally. Accordingly, the amount of data that can be stored in the buffer areas are reduced, thereby degrading the performance of the hard disk drive. Consequently, it would be desirable to provide an improved method for registering a defect map within a hard disk drive.